The present disclosure relates to a sheet conveying device for conveying a sheet of recording medium, and a sheet feed device and an image forming apparatus, each of which has the same.
Sheet conveying devices for conveying a sheet of recording medium from a sheet container where a plurality of sheets of recording media are placed are preferably adopted for image forming apparatuses. Known examples of an image forming apparatus of this type include a copier, a printer, a facsimile machine, and a multi-functional peripheral having functions of these machines. In an image forming apparatus, sheets of recording media are conveyed one by one from a sheet container to an image forming unit by a sheet conveying device. Then, an image is formed on a sheet of recording medium in the image forming unit.
In order to convey sheets one by one, the sheet conveying device includes a feed roller. In addition, a lift plate is arranged in the sheet container. When an end of the lift plate moves upward, the feed roller comes in contact with a top sheet among stacked sheets. As a result, the sheet is fed out by the feed roller.
In order to continuously convey the sheets placed in the sheet container, it is necessary to maintain an end of the lift plate to be in a lifted state. A technique for implementing such a state is known, in which a position of the lift plate moved upward is maintained by an electromagnetic solenoid, for example. In addition, a technique is known which raises a lift plate by a driving unit that rotationally drives a feed roller in order to replace a driving unit dedicated to moving the lift plate such as the above-described electromagnetic solenoid. With this technique, a biasing spring arranged under the lift plate always applies an upward force to the lift plate. Cams are arranged at both ends of a rotation shaft which supports the feed roller. The cams come in contact with both ends of the lift plate to restrict the lift plate from moving upward. The cams rotate following rotation of the feed roller and an end of the lift plate moves upward, accordingly. The end of the lift plate, which is linked to the rotation of the feed roller, repeats upward and downward movement synchronously with timing of feeding a sheet.
In the above-described techniques, vibrations occur at a time of the lift plate moving upward following the collision between a sheet and the feed roller. In order to lower an adverse effect due to such vibrations on formation of an image, a lever having an elastic member is arranged between the cams and the lift plate, for example. With a swing of the lever, the elastic member eases the collision. Accordingly, the vibration transmitted to the image forming unit is reduced.
Meanwhile, in order to reduce the number of parts used in a sheet conveying device, a driving unit rotationally driving a feed roller may also serve as a driving unit of other conveyance rollers arranged downstream of the feed roller in a sheet conveying direction. Examples of such a conveyance roller include a registration roller. When the driving unit rotationally driving the feed roller rotationally drives the registration roller, an amount of rotation of cams increases at a time of the lift plate moved upward by a biasing spring. As a result, the driving unit causes the feed roller and the registration roller to experience rotational variations. In this connection, malfunctions have occurred, in which conveyance and formation of an image on a sheet is unstable, which has been antecedently conveyed and is nipped by registration rollers.